Polyphosphates are desirable components in automatic dishwashing detergent compositions, they are very effective scale inhibitors, however they suffer one main drawback. Polyphosphates will over time hydrolyze to orthophosphate. Orthophosphate does not function as a scale inhibitor and will actually form scale with calcium (calcium phosphate). A similar problem occurs when the washing liquor contains high level of calcium or the liquor is otherwise underbuilt. Scale deposits not only give rise to filming and spotting on the dishware/tableware but also on the interior of the dishwashing machine, especially on the heater element (hydrolysis is favoured at high temperature), negatively influencing the efficiency of the dishwashing process.
Carbonates are also common components in automatic dishwashing detergent compositions, which can also give rise to scale problems and therefore, filming and spotting on the washed articles. Traditionally, the filming and spotting problems have been ameliorated by the use of salt in order to soften the water (that is to reduce the concentration of cations, specially Ca2+ and Mg2+) and by the use of rinse aid containing sequestrant, dispersant and surfactant which to some extent help to control the hardness of the ions present in the water and to reduce the surface tension of the dishwashing liquor, thus avoiding the formation of liquid droplets and allowing uniform drying of the washed utensils, ameliorating filming and spotting issues.
The use of sulfonated polymers to reduce scale formation in automatic dishwashing is known in the art. In EP-A-851,022 a polymer comprising an olefinically unsaturated carboxylic acid monomer and at least one monomer unit selected from copolymerizable sulfonated monomers, copolymerizable non-ionic monomer and mixtures thereof is used in a rinse composition for inhibiting scale. EP-A-1,111,037 describes a detergent tablet having two separate regions, one of the regions comprises materials that delays dissolution, said region can further comprise an anti-scalant agent.
WO-A-01/72941 discloses an automatic dishwashing composition comprising a detergency builder and at least one polymer comprising carboxylate groups and sulfonate groups. U.S. Pat. No. 6,191,088 discloses a powdered automatic dishwashing composition comprising a polymer containing sulfonic acid groups.
Traditionally, the machine dishwashing process involves the steps of dosing detergent into the dispenser at the beginning of each wash and filling the salt and rinse aid reservoirs at intervals are required. Some users may find it inconvenient to carry out all these steps and prefer a simpler process involving the use of a single product performing all the functions required for the dishwashing process. Unitised doses of dishwashing detergents are found to be more attractive and convenient to some consumers, additionally they avoid the need of the consumer to measure the product thereby giving rise to a more precise dosing and avoiding wasteful overdosing or underdosing. For this reason automatic dishwashing detergent products in tablet form have become very popular. Detergent products in pouch form are also known in the art.
The detergent dishwashing product is usually placed inside the dispenser and released during the main-wash cycle of the dishwashing process. However, the dispensers of some dishwashing machines are not completely water tight, mainly for two reasons, either the dispenser has some apertures allowing water ingress or the dispenser is sealed with a rubber band that can deform with time due to the high temperature of the dishwashing process. Water ingress into the dispenser can cause premature leaking of dishwashing product which is thus lost after the pre-rinse. This problem is especially acute in the case of liquid compositions having a low viscosity wherein a considerable amount of the product can be lost before the main-wash cycle. In the case of solid compositions water leaking into the dispenser can also be a problem, leading for example to the caking of the composition or to the lost of activity of some ingredients, such as bleach.